(1) Field of the Invention
The invention relates to a pretreatment system and method for recycling exhaust water, and more particularly to a system and method which can remove a substantial amount of silt or contamination in the exhaust water before forwarding the water into a water-purification equipment.
(2) Description of the Prior Art
For most countries, all-aspect management and reasoned allocation on domestic water resources are a crucial topic to all kinds of nations for ensuring continuing prosperity of economic development. To the authority, it is important to establish a complete package of regulations and laws, and also to carry out a solid plan of public elementary construction leading to form a complete reservation and utilization network of the domestic water resources. On the other hand, to the private institute and ordinary family, the policy for utilizing the water is to save the money without violating the laws.
As the economics grow, the need for the utility water is increased as well. In general, the conventional water-supply pattern that supplies water from the reservoirs directly into the water-consumed party is no more an if-and-only if condition that can guarantee sufficient supply of water. Especially in the district that locates intensively a lot of semi-conductor manufacturing factories or other water-consumed industries, an increasing need for stable utility water supply becomes an important issue that can never be neglected and needs to be resolved immediately.
Generally speaking, there are two measures to resolve the water shortage problem; one is to dig out more nature water resources, and another is to save the water consumption. However, in the case that the former measure is employed, it usually implies that huge budget, laboring, and time need to be involved. Apparently, that resolving the water shortage problem by further sourcing can meet the urgent need from the industries. Also, the uncertainty for large-scaled construction is usually high and makes the work unpredictable. On the other hand, the latter measure can be carried out immediately at the consumer end, and seems to be feasible to meet short-term shortage. Usually, the latter measure includes at least two resorts, cutting down the water usage and/or recycling the exhaust water.
To evaluate possible resolutions to save the water consumption, it is evident that, by cutting down the water usage, the freedom of using water is usually sacrificed and inconvenience in the normal living operation is also inevitable. On the other hand, it is believed that recycling the exhaust water is a better way nowadays to resolve the water shortage problem, especially for those industries using plenty of water. The basic idea to recycle exhaust water is to utilize a water-purifying process to revitalize the exhaust water back to an acceptable quality level compared to the water that is directly supplied from a reservoir. For industries, by recycling the exhaust water, the external water need can be greatly reduced and the manufacturing can be much controllable.
The present invention is an effort on providing an method and a system for recycling the exhaust water. The exhaust water can be the water from a texture factory, from the oceans, or from a contaminated or half-salted well. The technical fields related to the present invention include exhaust water treatment, water-purification process, and water quality-monitoring method. Following are brief introductions upon these three fields.
A. Exhaust Water Treatment
Conventionally, to improve the quality of exhaust water to a releasable level, it is usually seen that bio-treatment, chemical mixing, or active carbonating is used to de-contaminate the exhaust water before discharged to the oceans. Among these treatments, chemical mixing is the most popular method to apply, in which chemicals are used to mix with the exhaust water for forming filterable flocculent gels. Generally, chemical mixing process can be classified to a rapid mixing (or coagulation) and a slow mixing (or flocculation). The rapid mixing can have the benefit of thoroughly blending the chemicals and the exhaust water, and the slow mixing can have more processing time to allow the flocculent gels growing.
In conventional rapid mixing equipment, the reactor is an open continuous stirred tank reactor (CSTR), shaped as a cylindrical tank or a rectangular tank In the tank, the chemicals and the exhaust water are forced to mix and form a plurality of flocculent gels. However, CSTR provides an open system that is vulnerable to the ambience. Rain, sand, or other particles can contaminate further the exhaust water in the tank. Also, due to a large volume of the tank, a dead volume that cannot be reached by the stirred flow in the tank does always exist. Conventional measures to resolve this disadvantage are to increase the stirring capacity, to modify the interior of the tank for enhancing the turbulence inside the tank, and to adjust the amount and the ingredients of the chemicals. Nevertheless, any aforesaid resort does lead to the increase of the cost.
On the other hand, a conventional plug flow reactor (PFR) provides a closed pipe flow for mixing the chemicals and the exhaust water. The PFR does not include any stirring mechanism, so that the energy consumed can be reduced. However, in the PFR, the pipe-flow mixing of the chemicals and the exhaust water is inferior to that in a CSTR; so that the PFR is seldom seen in industrial practice.
B. Water-purification Process
The water-purification process is to filter out the minerals, bacteria, silt, and other pollutants in the water; for improving the water quality to an acceptable level compared to a drinking water. Equipment for this purpose includes an active carbon water-purification facility, a reverse osmosis system, or the like. However, ordinary water-purification equipment is usually aimed at purifying the water directly supplied from an external water pipe, not at treating the internal exhaust water. Thus, if applying conventional water-purification equipment directly to purify the exhaust water, plenty of energy and cost are usually needed for successfully completing a treating target; for the exhaust water is not the design object for such equipment to handle.
B. Water Quality-monitoring Method
Conventionally, a silt density index (SDI) is usually provided to evaluate the water quality. SDI can be derived as follows.   SDI  =            (                        1          -                                    t              0                                      t              15                                      15            )        xc3x97    100  
where t0 is the duration for a 500-ml sample water to pass a 0.45-xcexcm standard membrane, and t15 is the duration after a first 15-minute operational time for another 500-ml sample water to pass the standard membrane.
Though the SDI numbering can be effectively used to show the pollution of source water, yet it is incapable of showing the silt density difference among various exhaust waters. Empirically, while the sample water is filled with particles sized to 0.45-1.00 xcexcm, the standard membrane will be rapidly jammed and allow only extreme little water to pass through. As a consequence, the t15 will go extreme big, and make the SDI value reach its 6.67 upper bound. Therefore, regarding the exhaust water, the SDI is not a relevant scale to distinguish the pollution degree.
Further, the trend of the water-managing policy worldwide is led to persuade a higher recycle rate of exhaust water. For example, in Taiwan, a 1998 national conference on water resources has proposed to increase the enforced recycle rate of exhaust water to 65%, from a 31% previous rate By raising the enforced recycle rate of exhaust water, the industry does not only need to improve the water-purification equipment, but also need to retreat any possible internal exhaust water. Hence, to provide a pretreatment system and a method for recycling exhaust water before conventional water-purification equipment is extremely important, and has obvious advantage on cost down and meeting the government""s regulation
Accordingly, it is an object of the present invention to provide a pretreatment system and a pretreatment method for recycling exhaust water, which can purify the exhaust water to a water quality acceptable to ordinary water-purification equipment.
It is yet another object of the present invention to provide a pretreatment system and a pretreatment method for recycling exhaust water, in which a mixing piping with rough interior is applied to simulate a series of close micro CSTR""s for thoroughly blending the exhaust water and doping chemicals.
It is a further object of the present invention to provide a modified silt density index, which can be used to effectively monitor the pollution variation upon various exhaust water samples.
The pretreatment method for recycling exhaust water in accordance with the present invention is used to purify the exhaust water and to generate clean water for further supplying to a water-purification equipment. The pretreatment method comprises:
(A) Introducing the exhaust water and adding a substantial amount of chemicals to form a gel water;
(B) Flowing the gel water through a mixing piping, in which the gel water is stirred by a plurality of turbulent structures located inside the mixing piping for forming a plurality of flocculent gels;
(C) Leading the gel water through a filtering unit for filtering out the flocculent gels of the gel water and forming the output clean water; and
(D) Introducing the clean water to the water-purification equipment.
According to the present invention, the chemicals used in step (A) can be Al2(SO4)3.18H2O, PAC, FeCl3, and any chemical available in the art.
According to the present invention, the turbulent structures located inside the mixing piping in step (B) is used to simulate a series of in-pipe micro CSTR""s for forming a series of turbulent regions to thoroughly mix the exhaust water and the chemicals. The turbulent structures can be achieved by providing coarse interior to the mixing piping. Preferably, the mixing piping can be formed by worm pipes. Cross sections for the worm pipes can be a block-wave pattern, a sinusoidal-wave pattern, a triangular-wave pattern, or any pattern the like.
According to the present invention, in step (B) for providing in-pipe shearing to assist the stirring between the chemicals and the exhaust water, the mixing piping can be arranged to have a repeatedly bent appearance, or to surround the exterior of the filtering unit.
Preferably in the step (B), the duration for the gel water to flow through the mixing can be between 5 and 60 seconds.
In one embodiment of the pretreatment method for recycling exhaust water, the mixing piping in step (B) can be made as a pipe filled with interior stuffing for preventing laminar flow inside the pipe.
In one embodiment of the pretreatment method for recycling exhaust water, the filtering unit in step (C) can be an auto reverse-washing multi-media sand tank or the like filtering device. Typically, the sand tank can have three layers: a 5 mm-20 mm pebble bottom layer, a 1 mm-3 mm coarse crystal sand middle layer, and a 0.5 mm-1.5 mm fine crystal sand upper layer. The gel water is firstly introduced to the bottom layer, through the middle layer, and finally flows out of the tank from the upper layer.
In one embodiment of the pretreatment method for recycling exhaust water according to the present invention, an additional step (B1) can be processed between the step (B) and the step (C), which the step (B1) is to lead the gel water through a buffer tank for growing the flocculent gels in the gel water. In the buffer tank slow mixing of the chemical and the exhaust water is processed for a substantial duration of time. Preferably, the gel water is introduced into the buffer tank by a tangential direction; so that the gel water can circulate gradually inside the buffer tank. Preferably, the gel water is led into the buffer tank from a bottom thereof and led out of the buffer tank from a top thereof. In the embodiment, the buffer tank can be a cylindrical tank with a diameter-to-height ratio between 1 and 0.1. The gel water is preferably to flow in the buffer tank for 1 to 10 minutes.
In one embodiment of the pretreatment method for recycling exhaust water according to the present invention, an additional step (C1) can be processed between the step (C) and the step (D), which the step (C1) is to lead the gel water through at least a filter for protecting the water-purification equipment. The filter can include only a 5-xcexcm filter, or a 5-xcexcm filter and a 1-xcexcm filter.
The pretreatment system for recycling exhaust water, which is established to carry out the pretreatment method for recycling exhaust water in accordance with the present invention, can include:
an inlet piping, having a first inlet end for introducing the exhaust water into the inlet piping and a first outlet end;
a doping unit, for adding chemicals into the inlet piping to mix with the exhaust water for forming a gel water;
a mixing piping, having a second inlet end fluidly connected with the first outlet end of the inlet piping and a second outlet end, the mixing piping including coarse interior for generating a plurality of turbulent mechanism to form turbulent flow inside the mixing piping for helpfully promoting a plurality of flocculent gels to grow in the gel water;
a filtering unit, for removing the flocculent gels in the gel water, having a third inlet end fluidly connected with the second outlet end of the mixing piping and a third outlet end; and
an outlet piping, having a fourth inlet end and a fourth outlet end, fluidly connected with the third outlet end of the filtering unit and the water-purification equipment, respectively.
In one embodiment of the pretreatment system for recycling exhaust water according to the present invention, the doping unit can include a chemical tank and a doping pump for feeding the chemicals from the chemical tank into the inlet piping.
According to the present invention, the coarse interior of the mixing piping can be formed as a block wave-type interior, a sinusoidal wave-type interior, a triangular wave-type interior and any the like. Preferably, the mixing piping can be a worm pipe.
Preferably, the mixing piping can be wound around the filtering unit, or can be arranged by a serpentine style with a plurality of abrupt bent; for enhancing the in-pipe shearing to assist the forming of turbulent flow.
In one embodiment of the present invention, the mixing piping can be made as a pipe filled with interior stuffing for preventing laminar flow inside the pipe; thus thorough mixing between the exhaust water and the chemicals can be achieved.
In one embodiment of the present invention, the filtering unit is an auto reverse-washing multi-media sand tank or the like filtering device. Typically, the sand tank can have three layers: a 5 mm-20 mm pebble bottom layer, a 1 mm-3 mm coarse crystal sand middle layer, and a 0.5 mm-1.5 mm fine crystal sand upper layer. The gel water is firstly introduced to the bottom layer, through the middle layer, and finally flows out of the tank from the upper layer.
In one embodiment of the present invention, the pretreatment system for recycling exhaust water can further include a buffer tank fluidly inter-connected between the second outlet end of the mixing piping and the third inlet end of the filtering unit, for growing the flocculent gels. In the buffer tank, slow mixing of the chemicals and the exhaust water can be processed for a substantial duration of time. Preferably, the gel water is introduced into the buffer tank by a tangential direction; so that the gel water can circulate gradually inside the buffer tank. Preferably, the gel water is led into the buffer tank from a bottom thereof and led out of the buffer tank from a top thereof. In the embodiment, the buffer tank can be a cylindrical tank with a diameter-to-height ratio between 1 and 0.1. The gel water is preferably to flow in the buffer tank for 1 to 10 minutes.
In one embodiment of the present invention, the pretreatment system for recycling exhaust water can further include at least a filter fluidly inter-connected between the third outlet end of the filtering unit and the fourth inlet end of the outlet piping, for protecting the water-purification equipment. The filter can include only a 5-xcexcm filter, or a 5-xcexcm filter and a 1-xcexcm filter.
Further, on one embodiment of the present invention, the outlet piping of the pretreatment system for recycling exhaust water can include a monitoring sub-piping fluidly deviated from the outlet piping for monitoring a modified silt density index of the clean waterflowing through the outlet piping. The monitoring sub-piping further includes a pressure-adjusting unit and a standard membrane filter located downstream of the pressure-adjusting unit, and an outlet end of the standard membrane filter forming a drip outlet of the monitoring sub-piping thereof.
The modified silt density index (MSDI) for expressing a level of pollution upon a substantial amount of sample water from the outlet piping can be derived as:   MSDI  =            1              t        E              xc3x97    100  
where tE is a duration needed for a 100-ml of sample water passing a standard membrane filter to achieve a dripping rate lower than 15 drops per 5 seconds under 30 psi. Preferably, the standard membrane filter is a 0.45-xcexcm membrane filter.